1. Field of the Invention
The present invention relates to a LCD (Liquid Crystal Display) device. In particular, an active-matrix-type LCD device that operates in IPS (In-Plane-Switching) mode, so that a wide range of angles of visual field can be provided. The present invention also relates to a method of manufacturing the LCD device.
2. Prior Arts
There are generally two types of LCD devices: one with the TN (Twisted Nematic) mode and the other with IPS mode. Wherein, according to the TN mode, information is displayed through rotating molecule axes of respective oriented LCD device molecules in a direction perpendicular to a glass substrate, whereas, according to the IPS mode, it is done through rotating the molecule axes in a direction parallel to the glass substrate.
An LCD device with the IPS mode has a feature whereby a high quality display is maintained with less dependency upon the viewing angle. This emanates from the fact that even if the eyes of the viewer are moved, they end up looking at only the short axes of the liquid crystal molecule. This special feature results in providing the benefit of a much wider range of angles of visual field than that provided by an LCD device with the TN mode.
A conventional LCD device with the IPS mode providing a wide range of angles of visual field is disclosed in Publication of Examined Patent Application No. Sho-63-21907 and Publication of Unexamined Patent Application No. Hei-6-202127 (hereafter, referred to as Reference 1 and Reference 2, respectively). According to the LCD devices, as shown in these references, since a voltage, irrelevant to the display voltage corresponding to the image signal, is always applied between data bus lines (drain electrode lines), through which an image signal is transmitted, and its corresponding pixel electrode, the applied voltage causes an occurrence of an unnecessary electric field emitted from the data bus line. Wherein, this unnecessary electric field is applied to a liquid crystal layer. As a result, a problem will occur where the image display quality becomes poor.
Accordingly, in order to prevent the data bus line from emitting the unnecessary electric field, and it being applied to the liquid crystal layer, the LCD device, as illustrated in FIGS. 1 to 3 (hereafter, referred to as Reference 3) has been developed. Reference 3 is disclosed in Publication of Unexamined Patent Application No. Hei-10-186407 (Patent Application No. Hei-8-286381). Wherein, the data bus line, through which an image signal is transmitted, is formed above a common bus line that a reference voltage is applied to. In other words, by forming the data bus line so that it covers the entire common bus line, it is possible to shield the liquid crystal layer from the said unnecessary electric field.
FIG. 1 illustrates a partial layout of gate bus lines, data bus lines, a common electrode, and a common bus line in the LCD device as disclosed in Reference 3. FIGS. 2 and 3 are cross-sections along respective straight lines XXI to XXI and XXII to XXII in FIG. 1.
As illustrated in FIGS. 2 and 3, the LCD device is comprised of a glass substrate (hereafter, called TFT substrate) 113 with a matrix of multiple, thin-film transistors (hereafter, called TFT) 106, a glass substrate (hereafter, called CF substrate) 115 with a color filter layer 122, and a liquid crystal layer 118 placed between the substrates 113 and 115. The liquid crystal layer 118 is sealed by a sealing material (not shown in the figures), thus forming liquid crystal cell. This liquid crystal cell is filled with a liquid crystal and spacers.
Gate electrodes 107 of the respective TFT 106 are formed in a matrix on the TFT substrate 113. Multiple gate bus lines (gate electrode lines) 101 are formed so as to be connected electrically with the respective gate electrodes 107. Each of the gate bus lines 101 is connected to multiple gate electrodes 107 placed along each line in the TFT matrix. The multiple gate bus lines 101 are placed parallel to one another, and are also extended in the horizontal direction, as shown in FIG. 1. The gate electrodes 107 and gate bus lines 101 are both covered with a gate insulating film 111, which is formed on the surface of the TFTs substrate 113.
A drain electrode 108 and source electrode 109 corresponding to each gate electrode 107, and a patterned amorphous silicon layer 110 are all formed on the gate insulating film 111. A prospective to-be-generated, conductive channel, which plays the role of electrically connecting the drain electrode 108 and the source electrode 109, is formed inside the amorphous silicon layer 110. The gate electrode 107, its corresponding drain electrode 108 and source electrode 109, and a single amorphous silicon layer 110 comprise a TFT 106.
In addition, as shown in FIG. 2, multiple pixel electrodes 104 and multiple data bus lines 102 are formed on the gate insulating film 111.
As shown in FIG. 1, the multiple data bus lines 102 are parallel to one another extending in a vertical direction. Each data bus line 102 electrically connects the multiple drain electrodes 108 along each column in the TFT matrix, to one another.
Each pixel electrode 104 is placed at pixel region P, which is located between two adjacent gate bus lines 101 or between two adjacent data bus lines 102. It is connected electrically to the source electrode 109 of its corresponding TFT 106. The pixel electrodes 104 are each strip-shaped, each extending parallel to the data bus line 102 within corresponding pixel region P, in the vertical direction.
The TFT 106, the pixel electrode 104, the gate electrode 101, and the data bus line 102 are, as shown in FIGS. 2 and 3, covered with a inter-layer insulating film (passivation film) 112, which is formed on top of the gate insulating film 111.
As illustrated in FIG. 1, multiple common electrodes 105, and multiple common bus lines (common electrode lines) 103 extending in the horizontal direction are both formed on the surface of the inter-layer insulating film 112. Each common electrode 105 is strip-shaped, extending parallel to both the pixel electrode 104 and the data bus line 102 in a vertical direction. Each common bus line 103 connects the multiple common electrodes 105 to one another, and extends parallel to the gate bus line 101 in a horizontal direction.
As clearly shown in FIG. 1, each common electrode 105 is placed above its corresponding data bus line 102, and covers over this entire data bus line 102. Each common bus line 103 is placed in the vicinity of its corresponding gate bus line 101, but does not cover this gate bus line 101.
As shown in FIG. 2, a color filter layer 122 is formed on the surface of the CF substrate 115. The color filter layer 122 is comprised of a color material layer 116 and an over-coating layer 117, which protects the color material layer 116 and smoothes out the surface of the color filter 122. The color material layer 116 is comprised of color dot materials or color stripe materials of red, green, and blue, which are arranged and placed according to a certain regulation, and a black matrix 121, which is placed so as to fill-in among the red, green, and blue dot materials or stripe materials.
A predetermined selecting signal is applied to the gate bus line 101 (see FIG. 4A). thus switching on its corresponding TFT 106. Its corresponding image signal is applied (See FIG. 4B) to the data bus line 102 selected by the said selecting signal. A common reference voltage is applied to the multiple common bus lines 103 at the same time. The TFT 106 corresponding to the pixel selected by the selecting signal, which is applied to the gate bus line 101, turns on. As a result, a voltage corresponding to the image signal applied to the data bus line 102, is applied between its corresponding common electrode 105 and pixel electrode 104. This applied voltage causes the occurrence of an electric field parallel to both the TFTs substrate 113 and the CF substrate 115. Wherein, this electric field is applied to the molecules of the liquid crystal in the liquid crystal layer 118. This electric field allows the molecules of the liquid crystal to rotate by a certain degree of angle in conformity with the applied image signal. Consequently, an image corresponding to the applied image signal is displayed on the screen of the LCD device.
Since each TFT 106 has a so-called bottom gate structure, where the source electrode 109 and the drain electrode 108 are placed above the gate electrode 107, it is generally called a xe2x80x9creverse staggered structurexe2x80x9d.
According to the LCD device of Reference 3, as is apparent from FIG. 1, each common electrode 105 entirely covers its corresponding data bus line 102. Accordingly, an unnecessary electric field radiated from the data bus line 102, which is a problem with the LCD devices of References 1 and 2, can be virtually blocked by the common electrode 105. Therefore, a possible occurrence of degradation in the image display quality, due to the unnecessary electric field influences on the molecules of the liquid crystal in the liquid crystal layer 118, can be prevented.
However, the LCD device of Reference 3 has the following problem, whereby the quality of the displayed image is not satisfactory.
That is to say, since the color material layer 116 on the CF substrate 115, the black matrix 121. and the over-coating layer 117 remain in an electrically floating state, they tend to be easily polarized or electrically charged (see FIG. 5). In particular, the black matrix 121 tends to be very easily polarized or electrically charged. In addition, the black matrix 121 is conductive, therefore, an electric charge can easily move within it. This may cause the degradation in the quality of a displayed image. For example, the ends of the black matrix 121 may emit a light, or an image may be fixed on the screen of the LCD device. This problem will be described in more detail while referring to FIGS. 4A and 4B, hereafter.
According to the conventional LCD device in FIGS. 1 to 3, as disclosed in Reference 3, a selecting signal is applied to one of the gate bus lines 101. For example, a selecting signal 23 as shown in FIG. 4A, is a typical waveform. In this case, an image signal 24, as shown in FIG. 4B, is applied to the data bus line 102.
The scanning time per frame (Tframe) of the selecting signal 23 in FIG. 4A is equal to 16.6 ms. An ON-voltage Von of approximately 20 V of the selecting signal 23 is applied to one of the gate bus lines 101 within a selecting time Ton (=26 micro-seconds) during the scanning time, Tframe. An OFF-voltage, Voff, of approximately xe2x88x925 V is applied during the time except for the selecting time (Ton).
As shown in FIG. 5, an unnecessary electric field radiated from the gate bus line 101, while the above negative voltage of xe2x88x925 V is applied, influences the color material layer 116 of the CF substrate 115, the over-coating layer 117, and the black matrix 121. The electric field causes an occurrence of electrification and polarization in the color material layer 116, the over-coating layer 117, and the black matrix 121.
In particular, the black matrix 121 tends to be easily polarized. In addition, since it includes a material such as carbon, electric charges can easily move within the black matrix 121. This causes a degradation of the image display quality. For example, this causes an occurrence of a smear and/or a fixation of an image on the screen in the conventional LCD devices.
To prevent these problems from occurring, it is necessary to use, for example, a low-conductive and hard-to-be-polarized material for the black matrix 121.
Accordingly, an objective of the present invention is to provide an active-matrix-type LCD device, which displays an image of high quality.
Another objective of the present invention is to provide an active-matrix-type LCD device, which can control a possible influence caused by the occurrence of an unnecessary electric field, which is generated via an active element such as a TFT.
Furthermore, an objective of the present invention is to provide an active-matrix-type LCD device, which prevents an occurrence of a smear and a fixation of an image on the screen resulting from a possible charging and polarization in the black matrix.
Yet another objective of the present invention is to provide an active-matrix-type LCD device without a black matrix, which tends to easily cause the occurrences of a charging and polarization.
Yet another objective of the present invention is to provide a method of manufacturing the above LCD devices.
To attain the above objectives, according to an aspect of the present invention, an LCD device is provided, comprising a plurality of common electrodes (5), which cover a plurality of data bus lines (2), and a plurality of common bus lines (3), which cover a plurality of gate bus lines. An example of the liquid crystal display device is illustrated in FIG. 9. The above reference numerals put in the parentheses are attached to respective corresponding elements in FIG. 9.
According to an aspect of the present invention, an LCD device is provided, comprising a plurality of pixel electrodes (4), which cover a plurality of gate bus lines (1) and a plurality of data bus lines (2). An example of the liquid crystal display device is illustrated in FIG. 14.
According to an aspect of the present invention, a method of manufacturing an LCD device is provided, comprising a first forming step of forming a plurality of gate bus lines (7, 1) on a substrate; a second forming step of forming a plurality of pixel driving transistors (6), a plurality of pixel electrodes (4), and a plurality of data bus lines (2) on an insulating layer (11), which is formed on the said substrate; a third forming step of forming an inter-layer insulating film (12) on the resulting surface in the said second forming step; and a fourth forming step of forming a plurality of common electrodes (5) on the said inter-layer insulating film (12), so as to overlap both the said plurality of gate bus lines (7, 1) and pixel driving transistors (6), and also forming a plurality of common bus lines (3) on the said inter-layer insulating film (12), so as to overlap the said plurality of data bus lines (2). An example of a method of manufacturing a liquid crystal display device is illustrated in FIG. 25.
According to an aspect of the present invention, a method of manufacturing an LCD device is provided, comprising a first forming step of forming a plurality of gate bus lines (7, 1), a plurality of common electrodes (5), and a plurality of common bus lines (3) on a substrate; a second forming step of forming a plurality of pixel driving transistors (6) and a plurality of data bus lines (2) on an insulating layer (11), which is formed on the said substrate; a third forming step of forming an inter-layer insulating film (12) on the resulting surface in the said second forming step; and a fourth forming step of forming a plurality of pixel electrodes (4) on the said inter-layer insulating film (12), so as to overlap the said plurality of gate bus lines (7, 1), the said pixel driving transistors (6), and the said data bus lines (2). An example of a method of manufacturing a liquid crystal display device is illustrated in FIG. 26.